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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 1Submission NEW CHIP SPREADING SEQUENCES FOR TG1 MULTIPLE ACCESS IEEE P802.22 Wireless RANs Date: 2008-9-4 Authors : Notice: This document has been prepared to assist IEEE 802.22. It is offered as a basis for discussion and is not binding on the contributing individual(s) or organization(s). The material in this document is subject to change in form and content after further study. The contributor(s) reserve(s) the right to add, amend or withdraw material contained herein. Release: The contributor grants a free, irrevocable license to the IEEE to incorporate material contained in this contribution, and any modifications thereof, in the creation of an IEEE Standards publication; to copyright in the IEEE’s name any IEEE Standards publication even though it may include portions of this contribution; and at the IEEE’s sole discretion to permit others to reproduce in whole or in part the resulting IEEE Standards publication. The contributor also acknowledges and accepts that this contribution may be made public by IEEE 802.22. Patent Policy and Procedures: The contributor is familiar with the IEEE 802 Patent Policy and Procedures http://standards.ieee.org/guides/bylaws/sb-bylaws.pdf including the statement "IEEE standards may include the known use of patent(s), including patent applications, provided the IEEE receives assurance from the patent holder or applicant with respect to patents essential for compliance with both mandatory and optional portions of the standard." Early disclosure to the Working Group of patent information that might be relevant to the standard is essential to reduce the possibility for delays in the development process and increase the likelihood that the draft publication will be approved for publication. Please notify the Chairhttp://standards.ieee.org/guides/bylaws/sb-bylaws.pdf Carl R. StevensonCarl R. Stevenson as early as possible, in written or electronic form, if patented technology (or technology under patent application) might be incorporated into a draft standard being developed within the IEEE 802.22 Working Group. If you have questions, contact the IEEE Patent Committee Administrator at patcom@iee.org.patcom@iee.org > Soo-Young Chang, Huawei TechnologiesSlide 1Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 2Submission NEW CHIP SPREADING SEQUENCES FOR TG1 MULTIPLE ACCESS Soo-Young Chang Huawei Technologies September 2008 Soo-Young Chang, Huawei TechnologiesSlide 2 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 3Submission INTRODUCTION In D2 (and D4), one chip sequence was introduced for chip spreading, not for multiple access. [1] [2] However, with only one chip sequence multiple networks (or PPDs) in an area can not be facilitated. The author has introduced 8 orthogonal codewords (or seuences) in D3 to accommodate this multiple access feature. [3] In July 2008 meeting, Steve Kuffner [1] claimed these codewords in D3 do not have good correlation characteristics for chip synchronization and less uniform spectral characteristics. In this document, a new set of codewords are being introduced to improve these characteristics and meet the requirements. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 3 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 4Submission D2 CHIP SEQUENCE The spreading sequence for 802.22.1 D2 was a complex sequence that was chosen based on its correlation properties. Sequence = [1-j -1-j 1+j 1-j 1-j 1-j -1+j - 1-j] The figure was imported from [1]. It was plotted with average values with two cases of next bits 1 and -1. It means at one moment, the actual correlations may be larger than those shown in this figure. Still the value should be 2 for lags of 4 and -4. (any mistake in [1] ?) Autocorrelation values vs chip lag September 2008 Soo-Young Chang, Huawei TechnologiesSlide 4 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 5Submission D3 CHIP SEQUENCES The D3 spreading sequences were chosen to provide separability between different beacons operating in the same area on the same frequency. [3] The sequences in Table 26 of D3 are the inverted sense of the Hadamard 8 matrix: 1 1 1 1 1 1 1 1 1-1 1-1 1-1 1-1 1 1-1-1 1 1-1-1 1-1-1 1 1-1-1 1 1 1 1 1-1-1-1-1 1-1 1-1-1 1-1 1 1 1-1-1-1-1 1 1 1-1-1 1-1 1 1-1 Steve Kuffner claimed that these sequences have poor auto/cross-correlation properties, and are only ensured to be orthogonal when properly time aligned. [1] September 2008 Soo-Young Chang, Huawei TechnologiesSlide 5 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 6Submission INTRODUCTION OF NEW SEQUENCES A new set of four 8 chip sequences are being introduced where each element is a complex number. –Four sequences were selected so as for correlations to be less than 5.6 out of 16. C1:1-j -1-j 1+j 1-j 1-j 1-j -1+j -1-j C2:1-j 1+j 1+j -1+j 1-j -1+j -1+j 1+j C3:1-j -1-j -1-j -1+j 1-j 1-j 1-j 1+j C4:1-j 1+j -1-j 1-j 1-j -1+j 1-j -1-j September 2008 Soo-Young Chang, Huawei TechnologiesSlide 6 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 7Submission HOW TO CALCULATE CORRELATIONS (1) Received chip stream r1r2r3r4r5r6r7r8r9r10r11r12r13r14r15r16 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 Bit nBit n+1 Red chips are overlapped with chips for the next bit. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 7 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 8Submission HOW TO CALCULATE CORRELATIONS (2) Received chip stream r1r2r3r4r5r6r7r8r9r10r11r12r13r14r15r16 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 Bit nBit n+1 Each bit may have 1 or -1. If two adjacent bits are identical, red chips needs no inversion. If two adjacent bits are different values, red chips needs to be inverted to have lower correlations. In the scheme proposed, the smaller one is taken from these two cases as a correlation at a position. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 8 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 9Submission HOW TO CALCULATE CORRELATIONS (3) Take a block of eight chips randomly from the received chip stream. Calculate a correlation of this block with the assigned receiver sequence. a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 a1a2a3a4a5a6a7a8 Calculate two correlations by shifting by one chip at one time and by taking inversion and non-inversion for red chips. Take the smaller correlation value between two values with inversion and non- inversion for the correlation of the shifted block. For eight shifted sequences including no shift, get correlation values. The chip sequence with highest correlation value is the right one for bit synch. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 9 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 10Submission HOW TO GET BIT SYNCH If the receiver received chip stream which was spread with the same sequence, –Calculate a correlation between a received 8 chip sequence and the receiver’s assigned chip sequence. Correlations calculated for a chip sequence is explained in the previous three slides. –Calculate another correlation by shifting the received chip stream by one chip. –Using the above procedure, eight correlations are calculated. –Synchronize the chip stream with the highest correlation. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 10 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 11Submission CORRELATION PROPERTIES Auto-correlations –Correlations with the same sequence –For eight different lags (or shifts), correlations can be calculated. Cn(0)Cn*(k): correlation of Sequence n between with 0 shift and with k chip shift, where k=0, 1, …., 7 –High correlation means more possibility to have bit synchronization. Cross-correlation –Correlations with different sequences –For eight different lags (or shifts), correlations can be calculated. Cn(0)Cm*(k) : correlation between Sequence n with 0 chip shift and Sequence m with k chip shift, where k=0, 1, …., 7 –These correlations should be smaller not to synchronize with wrong sequences. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 11 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 12Submission AUTO-CORRELATIONS FOR D2 SEQUENCE For D2, average values are plotted. It means that actual values can be larger than these values. –For ex., for lag1, correlation value can be 4 with the probability of ½. By applying the procedure to calculate correlations of received sequences introduced in this document, less correlations are taken for unsynchronized sequence. Autocorrelation values vs chip lag Only two non-zero correlations for unsynchronized sequences by proposed procedure Original average correlation values for D2 September 2008 Soo-Young Chang, Huawei TechnologiesSlide 12 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 13Submission AUTO-CORRELATIONS OF NEW SEQUENCES (1) Lag seq 01234567 C1160004j000 C2160004j000 C31640-4+4j (5.6)* 4-4-4j (5.6)* 00 c416-404-4j (5.6)* 44+4j (5.6)* 04 * Absolute correlation values: |Rnm(k)| September 2008 Soo-Young Chang, Huawei TechnologiesSlide 13 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 14Submission AUTO-CORRELATIONS OF NEW SEQUENCES (2) September 2008 Soo-Young Chang, Huawei TechnologiesSlide 14 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 15Submission D2 CROSS-CORRELATIONS No need to have cross-correlations for original D2 sequence because there are not multiple sequences. With this sequence, multiple PPDs (or networks) can not be implemented. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 15 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 16Submission CROSS-CORRELATIONS OF NEW SEQUENCES (1) Lag seqs 01234567 C1C20404-4j (5.6)* 44-4j (5.6)* 04 C1C30-4-4+4j (5.6)* 4j444+4j (5.6)* 8 C1C4084+4j (5.6)* 444j-4+4j (5.6)* 4 C2C3084+4j (5.6)* -44-4j-4+4j (5.6)* 4 C2C404-4+4j (5.6)* -4j4-44+4j (5.6)* -8 C3C400004000 * Absolute correlation values: |Rnm(k)| September 2008 Soo-Young Chang, Huawei TechnologiesSlide 16 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 17Submission CROSS-CORRELATIONS OF NEW SEQUENCES (2) September 2008 Soo-Young Chang, Huawei TechnologiesSlide 17Submission lag

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 18Submission SPECTRAL CHARACTERISTICS D2 spectral characteristics –From Steve Kuffner’s document [1], the D2 spreading sequence spreads the energy out relatively uniformly across the chip rate bandwidth. –This sequence is exactly the same as Sequence 1 of the new sequences proposed in this document. Therefore the spectrum of D2 sequence is the same as that of Sequence 1 of the new sequences. Spectral characteristics of new sequences –Spectra of new sequences are plotted using simulations in the following slides. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 18 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 19Submission D2 SPECTRAL PROPERTIES From Steve Kuffner’s document, the D2 spreading sequence spreads the energy out relatively uniformly across the chip rate bandwidth. [1] This sequence is exactly the same as Sequence 1 of the new sequences proposed in this document. Therefore the spectrum of D2 sequence is the same as that of Sequence 1 of the new sequences. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 19 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 20Submission SPECTRAL PROPERTIES OF NEW SEQUENCES Seq 1Seq 2 Seq 4Seq 3 September 2008 Soo-Young Chang, Huawei TechnologiesSlide 20 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 21Submission CONCLUSIONS In this document, a new set of four sequences is introduced and a new procedure to calculate correlations for bit synchronization is proposed. –A new set of sequences are selected with a criterion of maximum correlation of 5.6 out of 16. With these four sequences, up to four PPDs (or networks) can be operated in an area simultaneously. –This feature should be implemented. A new procedure to calculate correlations enables us to have smaller correlations for unsynchronized and unmatched sequences. The four sequences proposed have almost the same level of correlations and spectra as D2 (and D4) sequence has: –Auto-correlation: D2: 4/16 maxnew sequences: 5.6/16 max –Cross-correlation: 8/16 max –Spectra: almost the same spectrum envelope across the chip rate bandwidth These feature will improve the performance. September 2008 Soo-Young Chang, Huawei TechnologiesSlide 21 doc.: IEEE 802.22-08/0251r0 Submission

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September 2008doc.: IEEE 802.22-08/0251r0 Soo-Young Chang, Huawei TechnologiesSlide 22Submission REFERENCES [1] IEEE 802.22-08/0119r0, Steve Kuffner, May 2008. [2]P802.22.1/D2, October 2007 [3]P802.22.1/D3, April 2008 September 2008 Soo-Young Chang, Huawei TechnologiesSlide 22Submission

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